UNITED STATES—It makes sense for flowers to bloom in spring. Winter is too cool, windy and damp for both flowers and the insects that pollinate many of them. By summer, successfully pollinated flowers have faded, are busy making seed to disperse in autumn. Some plants produce fruit to get birds and other animals to disperse their seed. There are certain advantages to blooming early in the spring.
Native plants that are endemic to chaparral climates are quicker with bloom, so that they finish before the air gets too arid. Desert plants might bloom for less than a week. Some tropical plants might bloom whenever they want to because they do not understand the concept of seasons, but they are not the prominent plants in our gardens. Therefore, flowers get scarce this time of year.
Besides the few perennials and annuals that bloom as long as the weather stays warm, there are not many plants that bloom reliably so late in summer. Belladonna lily, which is also known as naked lady, might be one of the flashiest, as its bright pink flowers bloom on top of bare stalks before the low basal foliage develops. It was actually dormant through the warmest part of summer.
Billowy and bold pampas grass flowers bloom this time of year, but are uncommon. The boldest type of pampas grass is too big and difficult to manage for home gardens. The smaller type has dingy tan flowers, and is so invasive and weedy that it is unavailable in nurseries. Those of us who have it in our gardens did not plant it. Other grasses with nice late flowers are not very colorful.
Russian sage has become one of the more popular late blooming perennials. More traditional Japanese anemone, goldenrod, lion’s tail and showy stonecrop all seem to have lost popularity over the years.
Mexican blue sage should bloom best late in summer, but often finishes sooner than expected. Yarrow often blooms later than expected, until summer ends. Marigold, blanket flower and some sunflowers bloom until frost. Chrysanthemums, whether grown as annuals or perennials, are just beginning late in summer.
Highlight: fernleaf yarrow
‘Moonshine’ is probably the epitome of fernleaf yarrow, Achillea filipendulina, even though it is technically a hybrid. From the middle to the end of summer, its three inch wide corymbs (flat-topped trusses) of tiny bright yellow flowers stand as high as three feet above ferny and gray basal foliage. Bloom is best in full sun and warm exposure. Established plants do not need too much water.
Most varieties of fernleaf yarrow also bloom with bright yellow or gold flowers. Some might bloom with pale yellow, rosy pink, pale pink, reddish, white or pink and white flowers. All are good cut flowers, and can be dried. Some varieties are more compact. The most compact varieties work nicely in planters of mixed perennials. Butterflies and hummingbirds find them wherever they are.
Pruning out deteriorating blooms may promote sporadic subsequent bloom until autumn. However, some plants may bloom all at once, and then not bloom again until the following summer. Large blooms on the most vigorous plants may need to be staked. New plants can be propagated by division from mature plants. ‘Moonshine’ and many other cultivars are sterile. Others might self sow.